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At least 307 records · Page 17Linked to original sources
PubMed2006

Aqueous synthesis of copper nanocubes and bimetallic copper/palladium core-shell nanostructures.

We have synthesized copper nanocubes with uniform shape and size and copper/palladium core-shell bimetallic nanostructures in high yield by a two-stage procedure in the presence of dodecyl benzene sulfonic acid sodium. The copper nanocubes with a slight hole in the centers of the six {100} surfaces was prepared at the first stage. Later, the bimetallic copper/palladium core-shell nanostructures formed on the basis of the successive reduction of H2PdCl4 and the Pd growth on the surfaces of the Cu seeds.

Journal Article↗
PubMed2006

Palladium nanostructures and nanoparticles from molecular precursors on highly ordered pyrolytic graphite.

Nanostructures and nanoparticles of palladium assembled on highly ordered pyrolytic graphite (HOPG) by the adsorption of palladium molecular precursors (MPs), in dichloromethane solutions, have been prepared. Self-assemblies of palladium nanostructures on HOPG were characterized by scanning electron microscopy (SEM), Auger electron spectroscopy (AES), transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. In this work, palladium rings had a wide variety of sizes in the nanometer range, and the ring/tube structures were preserved after a reductive process in which palladium metallic nanoparticles were formed. Noncircular structures were observed at HOPG defects and atomic step sites, as well. It is proposed that the observed ring formation of the palladium molecular precursors on HOPG substrates is related to the functional groups in the MPs, van der Waals interactions between particles and between particle-substrate, as well as the wetting properties of the solvent. In the present work, we illustrate several examples of the formation and characterization of palladium complex tubes and the resulting palladium rings, via the reduction process.

Journal Article↗
PubMed2006

Nanostructure and mechanical properties of polybutylacrylate filled with grafted silica particles.

We investigate the nanostructure and the linear rheological properties of polybutylacrylate (PBA) filled with Stöber silica particles grafted with PBA chains. The silica volume fractions range from 1.8 to 4.7%. The nanostructure of these suspensions is investigated by small-angle neutron scattering (SANS), and we determine their spectromechanical behavior in the linear region. SANS measurements performed on low volume fraction composites show that the grafted silica particles are spherical, slightly polydisperse, and do not form aggregates during the synthesis process. These composites thus constitute model filled polymers. The rheological results show that introducing grafted silica particles in a polymer matrix results in the appearance of a secondary process at low frequency: for the lowest volume fractions, we observe a secondary relaxation that we attribute to the diffusion of the particles in the polymeric matrix. By increasing the silica volume fraction up to a critical value, we obtain gellike behavior at low frequency as well as the appearance of a structure factor on the scattering intensity curves obtained by SANS. Further increasing the silica particle concentration leads to composites exhibiting solidlike low-frequency behavior and to an enhanced structure peak on the SANS diagrams. This quantitative correlation between the progressive appearance of a solidlike rheological behavior, on one hand, and a structure factor, on the other hand, supports the idea that the viscoelastic behavior of filled polymers is governed by the spatial organization of the fillers in the matrix.

Journal Article↗
PubMed2006

Facile method to prepare surface-enhanced-Raman-scattering-active Ag nanostructures on silica spheres.

In this paper we describe a very simple electroless plating method used to prepare Ag-coated silica beads. Robust Ag nanostructures can be reproducibly fabricated by soaking silica beads in ethanolic solutions of AgNO(3) and butylamine. When the molar ratio of butylamine to AgNO(3) is far below 1.0, distinct nanosized Ag particles are formed on the silica beads, but by increasing the amount of butylamine, network-like Ag nanostructures are formed that possess very broad UV/vis absorption characteristics extending from near-UV to near-infrared regions. In conformity with the UV/vis absorption characteristics, the Ag-deposited silica beads were highly efficient surface-enhanced Raman scattering (SERS) substrates, with the enhancement factor estimated using benzenethiol as a model adsorbate to be larger than 10(6). Since another silica layer can be readily deposited onto the Ag surface, the Ag-coated silica beads should be invaluable in the development of SERS-based biosensors.

Journal Article↗
PubMed2005

Near-field photochemical imaging of noble metal nanostructures.

The sub-diffraction imaging of the optical near-field in nanostructures, based on a photochemical technique, is reported. A photosensitive azobenzene-dye polymer is spin coated onto lithographic structures and is subsequently irradiated with laser light. Photoinduced mass transport creates topographic modifications at the polymer film surface that are then measured with atomic force microscopy (AFM). The AFM images correlate with rigorous theoretical calculations of the near-field intensities for a range of different nanostructures and illumination polarizations. This approach is a first step toward additional methods for resolving confined optical near fields, which can augment scanning probe methodologies for high spatial resolution of optical near fields.

Journal Article↗
PubMed2005

Femtosecond imaging of surface plasmon dynamics in a nanostructured silver film.

Light interacting with nanostructured metals excites the collective charge density fluctuations known as surface plasmons (SP). Through excitation of the localized SP eigenmodes incident light is trapped on the nanometer spatial and femtosecond temporal scales and its field is enhanced. Here we demonstrate the imaging and quantum control of SP dynamics in a nanostructured silver film. By inducing and imaging the nonlinear two-photon photoemission from the sample with a pair of identical 10-fs laser pulses while scanning the pulse delay, we record a movie of SP fields at a rate of 330-attoseconds/frame.

Electrons↗
PubMed2006

Self-assembled lamellar nanostructures of wholly aromatic rod-rod-type block molecules.

Wholly aromatic rod-rod type di- and triblock molecules, oligo(ether sulfone)-b-oligo(ether ketone)s (OES-OEK), were synthesized to study a solid-state self-assembled nanostructure. The OES and OEK segments in the block molecules form segregated crystalline domains. The energy-filtering transmission electron microscopy images revealed that the di- and triblock OES-OEK co-oligomers formed lamellar nanostructures with a periodicity of approximately 9 and 13 nm, respectively. [structure: see text].

Journal Article↗
PubMed2001

Nanostructure. Epitaxial diamond polytypes on silicon.

Carbon is unique in the variety of configurations it can adopt with itself and other elements. Here we show how ion beams can be used to nanostructure various diamond polytypes, epitaxially aligning them to a silicon substrate. The ready controllability of ion beams, which are already used to manufacture submicrometre-scale devices, means that our findings should enable new carbon and non-carbon materials to be nanostructured for a host of applications.

Journal Article↗
PubMed2004

Nanostructure engineering by templated self-assembly of block copolymers.

Self-assembling materials are the building blocks for bottom-up nanofabrication processes, but many self-assembled nanostructures contain defects and lack sufficient long-range order for certain nanotechnology applications. Here we investigate the formation of defects in a self-assembled array of spherical block-copolymer microdomains, using topographical templates to control the local self-assembly. Perfect ordered sphere arrays can form in both constant-width templates and width-modulated templates. For modulated templates, transition between configurations having a constant number of rows and configurations of stable arrays with varying numbers of rows is shown to be analogous to dislocation formation in an epitaxial thin film system. Based on the configuration transition energy and fluctuation energy, designed templates with a high tolerance for lithographical imperfections can direct precisely modulated block-copolymer nanostructures. This study provides insights into the design of hybrid systems combining top-down and bottom-up fabrication.

Nanotechnology↗
PubMed2004

Direct imaging and mesoscale modelling of phase transitions in a nanostructured fluid.

The kinetics of phase transitions is essential for understanding pattern formation in structured fluids. These fluids play a key role in the morphogenesis of biological cells, and they are very common in pharmaceutical products and plastic materials. Until now, it has not been possible to follow phase transitions in structured fluids experimentally in real time and with high spatial resolution. Previous work has relied on static images and indirect experimental evidence from spatially averaging scattering experiments. Simulating the processes with computer models is a further challenge because of the multiple time and length scales involved. Our movies based on in situ scanning force microscopy show the time sequence of the elementary steps of a phase transition in a fluid film of block copolymer from the cylinder to the perforated lamella phase. The movies validate a versatile simulation model that gives physical insight into the nature of the process. Our approach provides a means of improving the study and understanding of pattern formation processes in nanostructured fluids. We expect a significant impact on nanotechnology where block copolymers serve as self-organized templates for the synthesis of inorganic nanostructured materials.

Computer Simulation↗
PubMed2002

Confined supramolecular nanostructures of mesogen-bearing amphiphiles.

Stable surface nanostructures with different morphology have been successfully constructed by modifying the chemical structure of synthetic amphiphiles; by introducing mesogenic groups into bolaform amphiphiles, stable spaghetti-like or stripe-like nanostructures can be obtained; it is believed that such a kind of surface structure could be used for templating synthesis and assembly.

Journal Article↗
PubMed2006

Gold nanostructures: engineering their plasmonic properties for biomedical applications.

The surface plasmon resonance peaks of gold nanostructures can be tuned from the visible to the near infrared region by controlling the shape and structure (solid vs. hollow). In this tutorial review we highlight this concept by comparing four typical examples: nanospheres, nanorods, nanoshells, and nanocages. A combination of this optical tunability with the inertness of gold makes gold nanostructures well suited for various biomedical applications.

Biomedical Engineering↗
PubMed2003

Photonic nanopatterns of gold nanostructures indicate the excitation of surface plasmon modes of a wavelength of 50-100 nm by scanning near-field optical microscopy.

Scanning near-field optical microscopy images of metal nanostructures taken with the tetrahedral tip (T-tip) show a distribution of dark and bright spots at distances in the order of 25-50 nm. The images are interpreted as photonic nanopatterns defined as calculated scanning near-field optical microscopy images using a dipole serving as a light-emitting scanning near-field optical microscopy probe. Changing from a positive to a negative value of the dielectric function of a sample leads to the partition of one spot into several spots in the photonic nanopatterns, indicating the excitation of surface plasmons of a wavelength in the order of 50-100 nm in metal nanostructures.

Gold↗
PubMed2004

Searching for nanostructures of the cubic mesophase of liquid crystal molecules, BABH8.

Nanostructures of a thermotropic cubic phase forming liquid crystal compound, 1,2-bis-[4-n-octyloxy-benzoyl]-hydrazine was studied by molecular dynamics (MD) simulations. A model for its cubic phase structure was proposed, which was constructed from the building unit of a locally orientational ordered "bundle" consistent with the cell parameter and the space group (Ia3d) from the recent x-ray results. Stability of the model structure was studied by multinanosecond MD simulations. A periodic nanostructure with 2.6 nm periodicity [coincides with the Ia3d (211) reflection] was kept up to 60 ns in the reduced pressure simulation which realizes the experimental value of density. However, the calculated fourth-rank order parameter shows that the simulated final state above does not have cubic orientational symmetry but rather isotropic symmetry.

Journal Article↗
PubMed2004

Interfacial properties of the nanostructured dye-sensitized solid heterojunction TiO(2)/RuL(2)(NCS)(2)/CuI.

The interfaces of the nanostructured dye-sensitized solid heterojunction TiO(2)/Ru-dye/CuI have been studied using photoelectron spectroscopy of core and valence levels, x-ray absorption spectroscopy and atomic force microscopy. A nanostructured anatase TiO(2) film sensitized with RuL(2)(NCS)(2) [cis-bis(4,4(')-dicarboxy-2,2(')-bipyridine)-bis(isothio-cyanato)-ruthenium(II)] was prepared in a controlled way using a novel combined in-situ and ex-situ (Ar atmosphere) method. Onto this film CuI was deposited in-situ. The formation of the dye-CuI interface and the changes brought upon the dye-TiO(2) interface could be monitored in a stepwise fashion. A direct interaction between the dye NCS groups and the CuI is evident in the core level photoelectron spectra. Concerning the energy matching of the valence electronic levels, the photoelectron spectra indicate that the dye HOMO overlaps in energy with the Cu 3d-I 5p hydrid states. The CuI grow in the form of particles, which at the initial stages displace the dye molecules causing dye-TiO(2) bond breaking. Consequently, the very efficient charge injection channel provided by the dye-TiO(2) carboxylic bonding is directly affected for a substantial part of the dye molecules. This may be of importance for the functional properties of such a heterojunction.

Journal Article↗
PubMed2004

Abnormal IR effects of Pt nanostructured surfaces upon CO chemisorption due to interaction and electron-hole damping.

The abnormal IR effects (AIREs) characterized by a positive-going peak of platinum (Pt) nanostructured surface generated in a square-wave potential treatment upon CO molecule chemisorption was observed and analyzed with a consideration of the interparticle interaction and electron-hole damping between nanoislands and CO molecules. A theoretical simulation shows that the islanded nanostructured Pt surfaces, which gives rise to interparticle interaction, coupling with electron-hole mechanism, may contribute to the origins of positive-going peak (AIREs) observed by in situ Fourier transformation IR (FTIR) experiments.

Journal Article↗
PubMed2006

Imaging nanostructures with scanning photoionization microscopy.

We report detailed studies of local electronic properties in nanostructured thin metallic films using scanning photoionization microscopy. This novel form of microscopy combines the advantages of diffraction-limited optical excitation with the ability to detect both photons and low kinetic energy photoelectrons, permitting sensitive characterization of heterogeneous surfaces under vacuum conditions. Using this technique, correlated measurements of multiphoton photoemission cross section and optical penetration depth are reported for Au films supported on Pt. These results present a first step toward combining confocal fluorescence or Raman microscopy with time-resolved photoelectron imaging spectroscopy in complex metal film environments, which should be ideally suited to investigating local plasmonic effects in nanostructures.

Journal Article↗
PubMed2006

Positron annihilation studies of defects and interfaces in ZnS nanostructures of different crystalline and morphological features.

Nanostructures of ZnS, both particles and rods, were synthesized through solvothermal processes and characterized by x-ray diffraction and high resolution transmission electron microscopy. Positron lifetime and Doppler broadening measurements were made to study the features related to the defect nanostructures present in the samples. The nanocrystalline grain surfaces and interfaces, which trapped significant fractions of positrons, gradually disappeared during grain growth, as indicated by the decreasing fraction of orthopositronium atoms. The crystal vacancies present within the grains also trapped positrons. These vacancies further agglomerated into clusters during the thermal treatment given to effect grain growth. The positron lifetime was remarkably large at extremely small grain sizes (approximately 1.5 nm) and this was attributed to the occurrence of quantum confinement effects, as verified through optical absorption measurements. Positron lifetimes in ZnS nanorods increased with increasing content of cubic phase in the samples and this observation is assigned to the annihilation of positrons in sites with increased cubic unit cell volume. The Doppler broadened spectra also indicated qualitative changes consistent with these observations.

Journal Article↗